The objectives of this project are to assess changes in properties (number, affinity) of receptors in response to alterations in the environment, drug administration, stress, or hormones, and to develop methods for assessing receptor function in intact animals, in vivo. Stress or isoproterenol-induced reduction of adrenoceptors can be prevented by administration of quinacrine. The alpha-adrenoceptor mediated pressor responses to administered norepinephrine are of the alpha 2 type whereas different alpha 1-adrenoceptors (in the junction) respond to norepinephrine released from sympathetic nerves. Labelling of beta-receptors in vivo provides a means of measuring receptors in intact animals and humans.